Start off with replacing your shocks / struts. I recently installed some koni street shocks on a sport suspension 325ci. They are fairly inexpensive and are comparable to stock ride quality. While your in there, I'd probably replace the front and rear shock mounts, they are more than likely shot. Then you can look at the front control arms, front control arm bushings, sway bar end links, and tie rods. I would also look at replacing the rear trailing arm bushings. You can probably get most of these parts for under $1000 if you can install them yourself. And you will only have to do an alignment once and refresh your riding quality. You can look to see what else needs to be replaced when your under the car. The guibo is usually a 100k mile item. Also take a peek at your steering coupler while you have the front plate off. This should keep you busy..

But i have no more agree with you because this tire will be no more good on rough road. Suspension reduce the power of speed as well as engine power also reduced...